It is the dreaded condition that has affected about two million Britons but remains a mystery to scientists more than two years after it emerged.
Long Covid, which blights sufferers with months of headaches, muscle pain and disabling fatigue, struck down its many victims regardless of age, underlying health conditions or vaccination status.
But earlier this year, research published by Israeli scientists suggested that, for most people, it is now no longer a threat.
The study, of 3,000 people who had contracted Covid, found those given two vaccines were up to 70 per cent less likely to suffer long Covid than unvaccinated people.
British experts have since added that the UK’s triumphant vaccine programme, with more than half the population triple-jabbed and many receiving a fourth top-up dose, means protection against long-term symptoms could be even higher.
Long Covid, which blights sufferers with months of headaches, muscle pain and disabling fatigue, struck down its many victims regardless of age, underlying health conditions or vaccination status. But earlier this year, research published by Israeli scientists suggested that, for most people, it is now no longer a threat
But research published last week seemed to dash these hopes. A US study of more than 30,000 double-vaccinated people, documented in the journal Nature, found that two jabs reduced the risk of long-term symptoms by a meagre 15 per cent.
So what’s going on? And how worried do we need to be?
First, it’s important to define long Covid.
Patients can be split into two groups. The first comprises those who were hospitalised with serious Covid symptoms, and the second those whose Covid illness was initially mild but then lingered or even worsened.
Patients in the first group may have suffered serious damage to vital organs such as the lungs or heart. As a result, it can take months for them to recover. Because the Covid jabs are so effective at protecting against severe disease, doctors agree that there are now vanishingly few of these patients.
But the majority of the UK’s long Covid sufferers are in the second group. Some battle breathlessness and exhaustion, unable to work or complete simple tasks.
Doctors are still unsure what triggers the condition in these people, but there are several theories.
One is that symptoms are brought on by reservoirs of the virus that remain in certain areas of the body after infection. A US study in 2021 found that Covid cells remained in the gut months after infection.
Experts say that, if this is true, then it is possible anyone who gets infected, even the triple-jabbed, could still get long Covid. But the chances would be diminished.
‘The whole point of the Covid vaccines is that they train the immune system to find and destroy Covid in your body, so it’s likely that after three jabs the virus is going to find it hard to hide,’ says Dr David Strain, senior clinical lecturer at the University of Exeter Medical School. ‘But it is possible that, in small numbers, the virus could still slip past the immune system and remain in the body.’
Another theory is that the virus can cause the immune system to malfunction and attack healthy cells. If this is true, not only should three jabs reduce the risk of long Covid, it should also reduce how long sufferers feel unwell.
A US study of more than 30,000 double-vaccinated people, documented in the journal Nature, found that two jabs reduced the risk of long-term symptoms by a meagre 15 per cent. So what’s going on? And how worried do we need to be?
‘Vaccination prepares the immune system for the shock of Covid – which stops it going into overdrive when you get infected,’ says Professor Manoj Sivan, an expert in rehabilitation medicine at Leeds University. ‘If this theory is true, the immune system will be much more likely to return to normal function quickly.’
Dr Strain’s own research shows that the risk of developing the condition after two jabs is now just over nine per cent – the risk of developing it in the unvaccinated is roughly around 14 per cent. These figures follow on from analysis published in February by the UK Health Security Agency showed two vaccine doses reduced the risk of long Covid by about 40 per cent.
‘You’ve got to remember, you are also far less likely to catch Covid in the first place,’ says Dr Strain.
Worldwide, more than four in ten who caught Covid suffered symptoms for at least a month, a University of Michigan study found.
Experts say it is too soon to have exact data on the impact of three jabs on long Covid, but that it is likely to reduce the risk even more.
So why does it seem so many Britons are developing the condition?
Data from the Office For National Statistics suggests 1.3 million have experienced Covid symptoms for at least three months. And official figures suggest cases are not falling, but rising, at roughly the same rate as they did last year.
Experts say there is a simple explanation for this – long Covid is bound to rise with infection rates.
At the height of the Omicron wave in January, the UK saw more than 180,000 new cases a day. The incidence of long Covid rose too – but not dramatically.
‘The fact that long Covid patients rose steadily, but didn’t rocket like they did before we had vaccines, is proof the jabs are helping,’ says Dr Claire Steves, a clinical senior lecturer at King’s College London.
There are also question marks over the reliability of the Office For National Statistics figures, which are based on people’s own judgments about whether they have long Covid symptoms.
And experts say the multitude of problems linked to the condition, including fatigue, depression and concentration problems, could be caused by something else.
If true, many of these million cases may not be long Covid at all. ‘There are so many different symptoms of long Covid, but a lot of them are not specific,’ says Professor Francois Balloux, director of the University College London Genetics Institute. ‘Some people might get Covid and feel depressed afterwards because they are tired and don’t have motivation, which is quite normal when you get ill with any virus.’
And what of the US study that showed the jabs reduced the risk of long Covid by just 15 per cent?
‘This study has several major problems, which means it probably doesn’t give an accurate figure,’ says Prof Balloux.
‘It only looked at the condition in US army veterans, so people who are older than the average population, who are less likely to respond to the jabs in the first place. They also had greater odds of bad side effects from Covid, due to age.’
The risk of long Covid hasn’t gone away. Some studies suggest protection against infection can last up to a year after three jabs, but others say it could be more like three months for the more vulnerable.
A greater risk of infection means more chance of long-term symptoms developing.
‘Long Covid isn’t going anywhere, because Covid isn’t going anywhere,’ says Dr Steves.
How many are still catching the virus?
The number of people catching Covid has dropped dramatically since April, but last week it began to creep up once again.
Estimates suggest one in 65 people in England now have Covid, compared with one in 70 the week before. However, this is far below the number of cases seen in April, when as many as one in 13 had the virus.
Deaths continue to decrease, sitting at about 70 per day, but hospitalisations have also recently begun to rise. In the last week of May, the number of people admitted to hospital with Covid was at its lowest since July 2021 – fewer than 400 a day. But last Wednesday, hospitalisations rose to 600.
Experts say this is due to the rise of two new mutations of the highly transmissible Omicron variant.
The sub-types, labelled BA.4 and BA.5, are doubling in cases roughly every two weeks and could eventually replace the original Omicron sub-type. They are thought to be slightly more resistant to vaccines and more infectious.
However, scientists tracking Covid are not too concerned by the latest changes.
‘We should expect a mini- wave but nothing too dramatic,’ says Professor Francois Balloux, director of the University College London Genetics Institute. ‘Covid is always going to rise and fall as new variants arise. We should expect this to be the norm from now on.’